A unique process such as shown in U.S. Pat. No. 8,534,108 has become available for axially compressing shape memory alloy [SMA] wire to provide new and compact work output devices. The process is capable of plastic axial compression of continuous wire lengths in the martensitic phase causing it to elongate when heated to induce a phase transformation into the austenitic parent phase. In contrast, typically shape memory wire has been trained by stretching deformation in the martensitic phase so that it shortens when heated into the austenite phase. As a result, a new category of applications using axially compressed SMA wire in the form of super-elastic springs and SMA actuators has come into use. A long slender member such as a rod or wire (hereafter referred to as a wire) which is in a state of high axial compression stress and is changing in length without lateral structural support is subject to bending due to elastic instability (hereafter referred to as buckling). Thus, in these applications in which a portion of the wire must be free to axially expand and contract outside of the stationary lateral support provided for the wire and this portion of the wire will be called, “dynamic length”. Providing lateral support for the “dynamic length” portion of the wire results in the combined use of “dynamic anti-buckling support” with “a state of high axial compression stress” and “changing in length” applied to a “portion of the length of a long slender member (wire)”. Examples where all of these conditions exist simultaneously have not been reported in prior art except for those that were shown to exist in Austen U.S. Pat. No. 8,959,970, Method and Apparatus for Applying Uniaxial Compression Stressed to a Moving Wire. The only example in which these conditions exist are:
The shortening “changing in length” of “portion of the length of a long slender member, such as a shape memory wire, while it is in a state of high axial compression stress” caused by its: (a) being forcibly compressed in length in the martinsite state; or (b) being forcibly compressed in length in a compression test or forming (forging) operation while using “dynamic anti-buckling support” to prevent buckling.
One example of prior art is U.S. Pat. No. 3,724,336A by Fuchs in which dynamic anti-buckling support is provided for a long slender extrusion die rain with a high axial compression stress state, but a portion of the length of the ram does not change in length. This patent is directed to a collapsible feed mechanism for advancing and retracting a rod or rod like member which may be subjected to large compressive axial loads. This patent used a plurality of aligning plates “slidably” mounted in a support frame and they are articulated to maintain uniform spacing;
In Austen U.S. Pat. No. 8,959,970, Method and Apparatus for Applying Uniaxial Compression Stressed to a Moving Wire, paragraphs 0064 through 0070, a portion of the length of a long slender member, e.g. a shape memory metal wire experiences a changing length due to a high axial compression stress. However, the dynamic anti-buckling support is provided by a novel gripping action obtained by pressing the wire into a groove in the periphery of a moving wheel that push the wire into an anti buckling array of guide rollers that are positioned along an arc shaped path. There are few if any similarities of this method and apparatus to those of the invention described below in the present application;
There is a need of a means to provide lateral, anti-buckling support that accommodates the changing length of a wire segment while in a state of high axial compression stress. This change in length may be due to the wire elastically or plastically deforming with large (longitudinal) axial strains, the wire may be being pushed through a die in semi-continuous open die extrusion or be in other applications in which these conditions occur.